Method for forming ceramic films by anode-spark discharge

Abstract

A method for forming a ceramics film on the surface of a substrate comprises performing spark discharge in an electrolytic bath, wherein the electrolytic bath comprises an aqueous solution of a water-soluble or colloidal silicate and/or an oxyacid salt to which ceramics fine particles and/or specific fine particles are dispersed and the spark discharge is carried out in the electrolytic bath while ensuring the suspended state of the ceramics particles and/or the specific fine particles in the electrolytic bath. The method makes it possible to effectively form, on the surface of a metal substrate, ceramics films having a variety of color tones as well as excellent insulating properties and hardness. Moreover, it further makes it possible to effectively form a composite ceramics film having excellent wear resistance on the surface of a metal substrate.

What is claimed is: 
     
       1. A method for forming a ceramic film on the surface of a substrate by spark discharge performed in an electrolytic bath, said electrolytic bath consisting essentially of an aqueous solution of an oxyacid salt selected from the group consisting of tungstates, stannates, molybdates, borates, aluminates and phosphates in which fine ceramic particles having particle sizes ranging from 0.03 to 100 μm and selected from the group consisting of Al 2  O 3 , Al(OH) 3 , SiO 2 , 3Al 2  O 3 .2SiO 2 , TiO 2 , ZrO 2 , Cr 2  O 3 , SiC, TiC, TiN, TiB, ZrB, BN, WC, WSi 2 , and MoSi 2  are dispersed and the spark discharge being conducted in the electrolytic bath at a bath temperature ranging from 5° of 90° C. and a current density ranging from 0.2 to 20 A/dm 2  for not less than 5 minutes while ensuring the suspended state of the ceramic particles in the electrolytic bath. 
     
     
       2. The method of claim 1, wherein the concentration of the oxyacid salt in the aqueous solution used as the electrolytic bath ranges from 25 to 200 g/l. 
     
     
       3. The method of claim 1, wherein the particle size of the ceramic particles ranges from 0.03 to 20 μm. 
     
     
       4. The method of claim 1, wherein the amount of fine ceramic particles added to the electrolytic bath ranges from 5 to 100 g/l. 
     
     
       5. The method of claim 1, wherein the spark discharge is conducted at a bath temperature ranging from 15° to 60° C. and a current density ranging from 1 to 5 A/dm 2  for 10 to 60 minutes. 
     
     
       6. The method of claim 1, wherein the substrate is a metal substrate and the metal of the substrate on which the ceramic film is formed is a member selected from the group consisting of aluminum and alloys thereof, zirconium, titanium, niobium, magnesium and alloys thereof. 
     
     
       7. A method for forming a ceramic film on the surface of a substrate by spark discharge performed in an electrolytic bath, said electrolytic bath consisting essentially of an oxyacid salt selected from the group consisting of tungstates, stannates, molybdates, borates, aluminates and phosphates in which fine particles having particle sizes ranging from 0.01 to 100 μm and selected from the group consisting of molybdenum disulfide, carbon, fluorinated graphite and tetrafluoroethylene resin are dispersed and the spark discharge being conducted in the electrolytic bath at a bath temperature ranging from 5° to 90° C. and a current density ranging from 0.2 to 20 A/dm 2  for not less than 5 minutes while ensuring the suspended state of the fine particles in the bath. 
     
     
       8. The method of claim 7, wherein the particle size of the fine particles ranges from 0.03 to 20 μm. 
     
     
       9. The method of claim 7, wherein the spark discharge is conducted at a bath temperature ranging from 15° to 60° C. and a current density ranging from 1 to 5 A/dm 2  for 10 to 60 minutes. 
     
     
       10. The method of claim 7, wherein the amount of the fine particles added to the electrolytic bath ranges from 5 to 100 g/l. 
     
     
       11. The method of claim 7, wherein the substrate is a metal substrate and the metal of the substrate on which the ceramic film is formed is a member selected from the group consisting of aluminum and alloys thereof, zirconium, titanium, niobium, magnesium and alloys thereof. 
     
     
       12. A method for forming a ceramic film on the surface of a substrate by spark discharge performed in an electrolytic bath, said electrolytic bath consisting essentially of an oxyacid salt selected from the group consisting of tungstates, stannates, molybdates, borates, aluminates and phosphates in which fine ceramic particles having particle sizes ranging from 0.03 to 100 μm and selected from the group consisting of Al 2  O 3 , Al(OH) 3 , SiO 2 , 3Al 2  O 3 .2SiO 2 , TiO 2 , ZrO 2 , Cr 2  O 3 , SiC, TiC, TiN, TiB, ZrB, BN, WC, WSi 2  and MoSi 2  are dispersed and in which fine particles having particle sizes ranging from 0.01 to 100 μm and selected from the group consisting of molybdenum disulfide, carbon, fluorinated graphite and tetrafluoroethylene resin are dispersed and the spark discharge being conducted in the electrolytic bath at a bath temperature ranging from 5° to 90° C. and a current density ranging from 0.2 to 20 A/dm 2  for not less than 5 minutes while ensuring the suspended state of the fine particles in the bath. 
     
     
       13. The method of claim 7, wherein the fine particles are selected from the group consisting of molybdenum disulfide and tetrafluoroethylene resin.